Cardiac rate is influenced by sympathetic and vagal neural outflow from the central nervous system. This neural activity is the result of integration of information sent from many types of receptors in the periphery to the central nervous system. This study is an organized attempt to isolate the reflex effect of the carotid baroreceptors on the sympathetic and vagal outflow to heart. Once this is obtained, the influence of the information from many other receptors (including arterial chemoreceptors, cardiac receptors and lung receptors) on the reflex effects elicited by the carotid baroreceptors will be studied. The response of single fibers of the cardiac vagal and sympathetic nerves to mean blood pressure, pulsatile pressure, pulse rate will be assessed to determine which of these factors is important in regulating cardiac activity.